FOSSIL PLANTS. 481 



in proportion, while on the other side they have been relatively contracted and 

 widened. Without an examination of the shale at Newport, it would be diffi- 

 cult to account for such a metamorphosis. At this locality, the shales present 

 along the shore a series of low undulations, resembling slightly elevated waves ; 

 and there one can see that, in the state of fusion of the whole mass, the re- 

 mains of plants, following the force of upheaval, have been, at peculiar places, 

 drawn upwards and therefore elongated on one side, and of course drawn on 

 the other towards the rachis. It is peculiar that the rachis and stems do not 

 show any appearance of flexure and of deformation, and it is remarkable also 

 that the same phenomenon of dimorphism is not observable on the plants found 

 in the shale of the anthracite basin of Pennsylvania, where the flexures of the 

 veins of coal are often abrupt, and where traces of tortion are frequently seen 

 upon fragments of the combustible mineral. This deformation of vegetable 

 remains may give an idea of the difficulties encountered by the palaeontologist 

 in studying, as he has to do, mere fragments of plants in their fossil state. Not 

 only do these remains generally insufficiently represent the whole vegetable, 

 but often they are deformed by various forces and influences, to which they are 

 subjected in the process of mineralization. 



3. VEGETABLE REMAINS PRESERVED IN FERRUGINOUS 



CONCRETIONS. 



As far as we know, from the specimens abundantly found in Illinois, the 

 mode of preservation of fossil plants in concretions is somewhat different from 

 what it is in argillaceous shale. These concretions are found, especially in the 

 shale of Grundy county, irregularly scattered from top to bottom of the strata, 

 in the form of oval, more or less elongated, generally slightly flattened concre- 

 tions. They appear to have been formed by superposition of concentric layers 

 of slowly deposited carbonate of iron or ferruginous clay around central nu- 

 clei, which are most commonly parts of plants, bones of fishes or the remains 

 of insects and Crustacea. Their size and form vary according to that of the 

 body around which the deposit has been made. Some small leaflets of ferns are 

 found in nodules which are not larger than a walnut ; pieces of calamites are in- 

 closed in cylindrical concretions varying in length from two inches to one foot or 

 more ; pinnae of ferns or of Asteropliyllites have been discovered in flattened con- 

 cretions measuring about one square foot and only two inches thick, their form 

 agreeing more or less with that of the body around which they have originated, 

 though always showing an oval or round outline, by superposition of concentric 

 layers. It is not yet clear whether the flattening of some of the specimens is 

 the result of compression. Generally, the nodules which have cylindrical 

 pieces of stems, or nutlets for nuclei, are round or exactly oval, while they 

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